1. Field of the Disclosure
This disclosure relates generally to apparatus and methods for drilling wellbores.
2. Background of the Art
Oil wells (also referred to as “wellbores”) are drilled with a drill string that includes a tubular member having a drilling assembly with a drill bit at its bottom end. The tubular member is generally either a jointed pipe or coiled tubing. After the well or a section of the wellbore has been drilled, it is lined with a casing (also referred to as the liner). However, sometimes the liner is placed outside a portion of the drill string while drilling and may include a second drill bit, referred to as the reamer drill bit or reamer, above or uphole of the drill bit at the drilling assembly bottom (also referred to as the “pilot” drill bit). The pilot drill bit drills a bore with a certain diameter and the reamer enlarges this bore to the desired wellbore diameter. As the liner and pilot drill bit enter an unstable formation, the wellbore may collapse, causing damage to the portions of the drill string and drill bit located outside of the liner.